Non-alcoholic fatty liver disease (NAFLD) is a highly prevalent condition characterized by ectopic hepatic lipid accumulation in association with obesity and type 2 diabetes. A progressive derangement of hepatic energy metabolism underlies the progression of simple fatty liver to non-alcoholic steatohepatitis (NASH), a condition that carries high risk for progression to critical liver disease states. Unfortunately, the current method for monitoring NAFLD is liver biopsy, which has major limitations especially its high degree of invasiveness. Hyperpolarized 13C magnetic resonance imaging (MRI) is an emerging molecular imaging modality with a unique capability to access intermediary energy metabolism in a non-invasive manner, which is currently undergoing translation into human studies at several sites internationally in studies of cancer and cardiovascular disease. The goal of this new R01 project is to investigate a new application of this new molecular imaging modality to the assessment of NAFLD. The association between detected changes in hyperpolarized 13C MRI and progression of NAFLD will first be investigated in a preclinical model of the progression of NAFLD to NASH (Aim 1), specifically Zucker diabetic fatty (ZDF) rats fed a high fat diet. Two promising hyperpolarized probes of hepatic energy metabolism, [1- 13C]pyruvate and [2-13C]dihydroxyacetone, will be applied to these studies. These new hyperpolarized markers will be compared against gold standard measures of NAFLD derived from pathology, as well as biochemical assays of hepatic energy state and oxidative stress. Next, novel MRI methods will be developed to enable clinical translation of hyperpolarized 13C imaging of the liver (Aim 2). The proposed approach aims to enable dynamic free-breathing imaging of the entire liver by accelerated echo planar imaging (EPI) acquisition with sixteen-channel parallel imaging. To address the key challenge of array sensitivity calibration, a highly novel approach to parallel imaging will be deployed based on continuous tracking of receiver coil positions using an integrated manganese-55 MRI based fiducial marker system. Finally, initial clinical hyperpolarized [1- 13C]pyruvate MRI will be performed in normal subjects and patients with simple steatosis and NASH, with comparison to liver biopsy (Aim 3). By the end of this new five-year R01 Research Project Grant, we aim to deliver a valuable new clinical tool for non-invasively assessing the progression of NAFLD based on associated metabolic changes measured using hyperpolarized 13C MRI.